Protein-Based Drug Delivery Nanoparticles*

Elastin-like polypeptides (ELPs) are a class of biopolymers that undergo a reversible phase transition occurring at a transition temperature. Recently, six-armed star polymers (G10 and G19) have been synthesized with arms composed of ELPs, namely repeats of the amino acid sequence GVGVP. Each arm of the G10 contains 10 repeats of this sequence, whereas the G19 contains 19 repeats. Above a certain temperature, these proteins aggregate due to the hydrophobic nature of ELP chains. They form specific aggregation structures, which may prove suitable for drug delivery applications. The proteins may collapse into individual molecules or assemble into nanoparticles that could be used to transport and protect slightly hydrophobic drug compounds. We have characterized the solution properties of G10 and G19. The transition temperatures of the proteins were measured using spectrophotometry for various protein concentrations, salt concentrations, and pH values. The samples were also investigated using light scattering. In particular, dynamic light scattering was used to probe the size of the aggregates above and below the transition temperature. Further measurements illustrate the effects of salt concentration and pH on particle dimensions.